4.Chemical Bonding and Molecular Structure
medium

Stability of the species $Li_2, Li_2^-$ and $Li_2^+$ increases in the order of :

A

$Li_2 < Li_2^+ < Li_2^-$

B

$Li_2^- < Li_2^+ < Li_2$

C

$Li_2 < Li_2^- < Li_2^+$

D

$Li_2^- < Li_2 < Li_2^+$

(JEE MAIN-2013)

Solution

Correct option

(b) $\mathrm{Li}_{2}-<\mathrm{Li}_{2}^{+}<\mathrm{Li}_{2}$

Explanation:

$\mathrm{Li}_{2}(3+3=6)=\sigma 1 \mathrm{s}^{2}, \quad \hat{\sigma} 1 \mathrm{s}^{2}, \sigma 2 \mathrm{s}^{2}$

Bond order $=\frac{N_{b}-N_{a}}{2}=\frac{4-2}{2}=1$

$\mathrm{Li}_{2}^{+}(3+3-1=5)=\sigma 1 \mathrm{s}^{2}, \dot{\sigma}^{2} 1 s^{2}, \cdot \sigma 2 s^{1}$

Bond order $=\frac{3-2}{2}=\frac{1}{2}=0.5$

Bond order $=\frac{4-3}{2}=\frac{1}{2}=0.5$

Stability order is $\mathrm{Li}_{2}>\mathrm{Li}_{2}^{+}>\mathrm{Li}_{2}^{-}$ (because Li $_{2}^{-}$ have more number of electrons in antibonding orbitals which destabilises the species).

Standard 11
Chemistry

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